1. Technical Field
The present invention relates to engine stroke determination apparatuses, and more particularly, to an engine stroke determination apparatus capable of making a determination with a high degree of accuracy using a simple configuration.
2. Related Art
A four-stroke general purpose engine used in industrial field is requested to determine a stroke for the purpose of improving fuel efficiency and emission performance thereby not performing ignition in an exhaust stroke (wasteful ignition) to prevent after-burns in which unburned fuel is burned in an exhaust system and performing fuel injection only in an intake stroke instead of performing so-called fuel injection in every stroke.
For example, Japanese Unexamined Patent Application Publication (JP-A) No. 2009-236036 discloses a conventional technique relating to such engine stroke determination. Specifically, a pulse generation unit is provided to generate a pulse signal in accordance with the rotation of a crank shaft, and a duration of a pulse interval is measured with a microcomputer, whereby a compression stroke and an exhaust stroke are determined.
In addition, JP-A No. 2002-54493 indicates a technique in which a stroke is determined by measuring a discharge time of an ignition coil of a transistor ignition device.
However, in the technique described in JP-A No. 2009-236036, it is necessary to provide the pulse generation unit in the engine, which increases the number of components and makes the structure complicated.
In the technique described in JP-A No. 2002-54493, it is necessary to provide a timer function in the microcomputer to measure the discharge time of the ignition coil accurately, which makes the configuration of the apparatus complicated. In addition, it is necessary to set a strict threshold value of the discharge time for the determination: if the threshold value is inappropriate, the determination may be made falsely.